Trouble modifying Incremental Refresh Effective Date through XMLA

I'm trying to modify the Effective Date of an Incremental Refresh in SSMS using the XMLA endpoint as referenced here: https://docs.microsoft.com/en-us/power-bi/service-premium-incremental-refresh#xmla-endpoint-benefits-for-incremental-refresh

Here's my TMSL:

{
"refresh": {
"type": "full",

"applyRefreshPolicy": true,
"effectiveDate": "12/31/2020",

"objects": [
{
"database": "IncrementalRefreshTest",
"table": "IncrementalTest"
}
]
}
}

And the error:

The JSON DDL request failed with the following error: The 'Name' property cannot contain any of the following characters: . , ; ' ` : / \ * | ? " & % $ ! + = ( ) [ ] { } < >.

Technical Details:
RootActivityId: db374716-2de7-48aa-85b8-6317d4dc7791
Date (UTC): 4/3/2020 4:56:31 PM
0: PFError::SetLastError() line 2388 + 0x0 (sql\picasso\engine\src\pf\eh\pferror.cpp)
1: PFSetLastError() line 3135 + 0x0 (sql\picasso\engine\src\pf\eh\pferror.cpp)
2: ConvertExceptionsToPFResult<<lambda_b213bf727d7d4675491088f28b96fa88> >() line 388 + 0x34 (sql\picasso\engine\src\pf\kernel\shared\pfshmacros.inl)
3: PFSetLastErrorExTag() line 3727 + 0x21 (sql\picasso\engine\src\pf\eh\pferror.cpp)
4: 0x00007FFA7ED89A9E (symbolic name unavailable)

Session cancelled per end session header in user request.
0: PFError::SetLastError()+0x2e1
1: PFSetLastError()+0x4c9
2: PXSession::InternalExecuteCommand()+0xe50
3: PCSession::ExecuteCommand()+0xb4
4: PCClientRequestHolder::ExecuteRequest()+0xe7
5: PCRequestHolder::ExecuteTask()+0xbf
6: PFThreadPool::ExecuteJob()+0x4b8
7: PFThreadPool::WorkerMethod()+0x2f5
8: PFCommandThreadPool::ThreadProc()+0x21
9: PFThreadPool::ThreadProcWrapperForPFThreadPool()+0xb3
10: o_exp()+0x5a
11: BaseThreadInitThunk()+0x14
12: RtlUserThreadStart()+0x21

Session cancelled per end session header in user request.
0: PFError::SetLastError()+0x2e1
1: PFSetLastError()+0x4c9
2: PCClientRequest::OnRequestError()+0x1b7
3: PCClientRequestHolder::OnRequestError()+0x74
4: PCRequestHolder::ExecuteTask()+0x36a
5: PFThreadPool::ExecuteJob()+0x4b8
6: PFThreadPool::WorkerMethod()+0x2f5
7: PFCommandThreadPool::ThreadProc()+0x21
8: PFThreadPool::ThreadProcWrapperForPFThreadPool()+0xb3
9: o_exp()+0x5a
10: BaseThreadInitThunk()+0x14
11: RtlUserThreadStart()+0x21

I'd appreciate any help you could give.  Thanks